An Estimate of the Minimum Amount of Unsaturated Fatty Acid Required for Growth of Escherichia coli

Abstract

Abstract A temperature-sensitive unsaturated fatty acid auxotroph was used to demonstrate that the fabA gene of Escherichia coli is the structual gene for the β-hydroxydecanoyl thioester dehydrase studied by Bloch and co-workers. This mutant, which requires an exogenous source of unsaturated fatty acid for growth at temperatures above 36°, possesses a dehydrase activity of greatly increased thermolability. Analysis of fab+ and fab- transductants and of fab+ revertants indicate that the temperature-sensitive dehydrase activity is responsible for the growth phenotype of this strain. This mutant was then used for an estimation of the minimum amount of unsaturated fatty acid needed for growth. Due to its temperature-sensitive phenotype, at semipermissive temperatures the strain grows at a subnormal rate due to a reduced rate of unsaturated fatty acid synthesis. Under such conditions, a minimum amount of unsaturated fatty acid is reached which is 15 to 20% of the total phospholipid fatty acid. No marked accumulation of short chain saturated fatty acids is seen during growth at semipermissive temperatures. A similar study with another strain showed that the minimum content of unsaturated fatty acid needed for growth is largely independent of the ratio of palmitoleate to cis-vaccenate in the phospholipids. These results are discussed in terms of the role of unsaturated fatty acids in membrane structure and function and also in terms of the control of fatty acid synthesis.